[clang-scan-deps] add skip excluded conditional preprocessor block preprocessing optimization
This commit adds an optimization to clang-scan-deps and clang's preprocessor that skips excluded preprocessor
blocks by bumping the lexer pointer, and not lexing the tokens until reaching appropriate #else/#endif directive.
The skip positions and lexer offsets are computed when the file is minimized, directly from the minimized tokens.
On an 18-core iMacPro with macOS Catalina Beta I got 10-15% speed-up from this optimization when running clang-scan-deps on
the compilation database for a recent LLVM and Clang (3511 files).
Differential Revision: https://reviews.llvm.org/D67127
llvm-svn: 371656
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index d9a98dc..a4ac950 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -370,6 +370,37 @@
return DiscardUntilEndOfDirective().getEnd();
}
+Optional<unsigned> Preprocessor::getSkippedRangeForExcludedConditionalBlock(
+ SourceLocation HashLoc) {
+ if (!ExcludedConditionalDirectiveSkipMappings)
+ return None;
+ if (!HashLoc.isFileID())
+ return None;
+
+ std::pair<FileID, unsigned> HashFileOffset =
+ SourceMgr.getDecomposedLoc(HashLoc);
+ const llvm::MemoryBuffer *Buf = SourceMgr.getBuffer(HashFileOffset.first);
+ auto It = ExcludedConditionalDirectiveSkipMappings->find(Buf);
+ if (It == ExcludedConditionalDirectiveSkipMappings->end())
+ return None;
+
+ const PreprocessorSkippedRangeMapping &SkippedRanges = *It->getSecond();
+ // Check if the offset of '#' is mapped in the skipped ranges.
+ auto MappingIt = SkippedRanges.find(HashFileOffset.second);
+ if (MappingIt == SkippedRanges.end())
+ return None;
+
+ unsigned BytesToSkip = MappingIt->getSecond();
+ unsigned CurLexerBufferOffset = CurLexer->getCurrentBufferOffset();
+ assert(CurLexerBufferOffset >= HashFileOffset.second &&
+ "lexer is before the hash?");
+ // Take into account the fact that the lexer has already advanced, so the
+ // number of bytes to skip must be adjusted.
+ unsigned LengthDiff = CurLexerBufferOffset - HashFileOffset.second;
+ assert(BytesToSkip >= LengthDiff && "lexer is after the skipped range?");
+ return BytesToSkip - LengthDiff;
+}
+
/// SkipExcludedConditionalBlock - We just read a \#if or related directive and
/// decided that the subsequent tokens are in the \#if'd out portion of the
/// file. Lex the rest of the file, until we see an \#endif. If
@@ -396,6 +427,11 @@
// disabling warnings, etc.
CurPPLexer->LexingRawMode = true;
Token Tok;
+ if (auto SkipLength =
+ getSkippedRangeForExcludedConditionalBlock(HashTokenLoc)) {
+ // Skip to the next '#endif' / '#else' / '#elif'.
+ CurLexer->skipOver(*SkipLength);
+ }
while (true) {
CurLexer->Lex(Tok);